Autoclave reactors have a wide range of applications in chemical processes. A typical autoclave has one or more compartments and operates at elevated pressures and temperatures. Most autoclaves are heated by steam injection, autogenous heat generated by reactions within the autoclave, or by a combination of both.
In most applications, autoclaves are stirred, multi-compartment reactors. An example of a multi-compartment, cylindrical autoclave is shown in FIGS. 1 and 2. The reactor 100 has a plurality of compartments 104a-f, each compartment 104 having at least one agitator 108a-g. In most applications, the agitators 108a-g rotate in the same direction. Adjacent compartments 104a-f are separated by a divider 112a-3 configured as an overflow weir. The input slurry 116 moves from compartment to compartment by overflowing the weirs as shown by the arrows in FIG. 1. To permit cascading flow of the slurry from compartment to compartment, the liquid level in the various compartments varies in a step-wise fashion, with the first compartment 104a having a higher liquid level than the second compartment 104b, the second compartment 104b having a higher liquid level than the third compartment 104c, and so on, with the sixth compartment 104f having the lowest liquid level.
An example of an overflow weir-type divider 112 is shown in FIG. 2. The divider 112 is cylindrically shaped to match the cylindrical profile of the autoclave and has a notch 200 located at the top of the divider. Liquid flows though the notch to move to the next (downstream) compartment. There is a sufficient height differential between notches in consecutive overflow weirs so that backmixing of liquid cannot occur and positive flow and flow through the vessel is maintained. To provide the desired step-wise gradient in liquid levels from compartment to compartment, the heights of the notches 200 in the compartments vary in the same manner as the liquid level, with the notch 200 in the first divider 112a between the first and second compartments being higher than the notch 200 in the second divider 112b, which in turn is higher than the notch in divider 112c and so on.
An example of a typical chemical reaction for an autoclave reactor is the pressure oxidation of sulfide sulfur to cause dissolution and/or liberation of base and precious metals from sulfide sulfur compounds. Pressure oxidation is typically performed by passing the input slurry 116, which contains a base and/or precious metal-containing material (such as base and/or precious metal ores and concentrates), through the sealed autoclave (operating at superatmospheric pressure) and sulfuric acid. To provide for oxidation of the sulfide sulfur in the slurry, a molecular oxygen-containing gas 120 is typically fed continuously to the autoclave by means of a sparge tube (not shown) located below each agitator. The molecular oxygen and elevated temperature cause relatively rapid oxidation of the sulfide sulfur to form sulfuric acid and the metal sulfides to form metal sulfates, which are soluble in the acidic slurry, thereby forming a pregnant leach solution. The pregnant leach solution, which commonly contains from about 10 to about 100 grams/liter sulfuric acid, from about 5 to about 100 grams/liter dissolved metal, and from about 4 to about 50% solids by weight, is removed from the last compartment of the autoclave as an output slurry 124. Additional details about this process are discussed in U.S. Pat. No. 5,698,170 to King, which is incorporated herein by reference. To maintain a desired pressure and atmospheric gas composition in the autoclave, the gas in the autoclave is continuously or periodically vented as an off gas 128. One autoclave configuration is discussed in U.S. Pat. Nos. 6,368,381 and 6,183,706.
In designing an autoclave reactor, there are a member of considerations. For example, it is desirable that the slurry have an adequate residence time in each of the compartments. Short circuiting, or moving to the next compartment with an unacceptably short residence time in a compartment, can cause a substantial decrease in metal extraction levels. For best results, the Residence Time Distribution or RDT in each compartment should be as close as possible to ideal plug flow conditions. It is desirable to have, in each compartment, sufficient power input and mixing efficiency to provide a high degree of reaction of the molecular oxygen with sulfide sulfur. To provide a high mixing efficiency, it is common practice to impart high levels of power to the agitators, thereby causing a highly turbulent surface in each compartment.